The disclosure of Japanese Patent Application No. 2007-188654 filed on Jul. 19, 2007, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a fuel injection control apparatus and a fuel injection control method for an internal combustion engine.
2. Description of the Related Art
Conventionally, an internal combustion engine may be equipped with a fuel injection valve that is coupled to a common rail and performs a pilot injection during a compression stroke of the engine and then performs the main injection when the piston is near top dead center in the compression stroke.
However, when the pilot injection is performed, the fuel pressure in the fuel injection valve pulsates. Therefore, there is a brief period where the fuel pressure in the fuel injection valve deviates from a normal fuel pressure. If the main injection is performed during this period, the amount of fuel actually injected during the main injection may deviate from a normal fuel amount.
On the other hand, an error in the amount of fuel actually injected through main injection with respect to the normal fuel amount is determined in accordance with an interval between pilot injection and main injection. That is, the error can be obtained in advance as a function of the interval. Thus, some internal combustion engines are designed to calculate the interval between the pilot injection and the main injection, calculate the error in the main fuel injection amount in accordance with the calculated interval, and correct the main fuel injection amount in accordance with the calculated error (see Japanese Patent Application Publication No. 2005-240755 (JP-A-2005-240755)).
In the above described internal combustion engine, the interval is calculated from the difference between the target pilot injection timing and the target main injection timing. However, the actual main injection timing or the actual pilot injection timing may not always coincide with the corresponding target timing. Accordingly, there is an apprehension that the actual interval may be different from the calculated interval. On the other hand, the error in the fuel injection amount for main injection results from pulsations of the fuel pressure in the fuel injection valve and therefore can greatly change even if the interval changes only slightly. Then, in the aforementioned internal combustion engine, the error in the fuel injection amount for main injection cannot be accurately calculated with ease, and therefore, there is a high likelihood that the actual fuel injection amount during main injection cannot be held equal to the normal amount with ease.